Kirito is someone who is not good with words and can be quite direct. This is in-part due to him not having many friends and shutting himself off from others as a side-effect of his love for computers. As such, he can come off as a rude person to others and sometimes actually appears to enjoy angering and teasing people. He can also come off as being overconfident in thinking he can accomplish what no-one else can with little to no effort on his part.

He is almost always a calm and collected character, rarely showing any signs of distress. When Kayaba Akihiko appeared in SAO and announced that the virtual world he had entered had become a Death Game, Kirito showed only a slight reaction and was able to quickly accept the new conditions of the game while many others panicked all around him. He has shown different moods throughout the series; at times being rather cheerful, while being gloomy at others. When in a battle, he becomes incredibly fierce and aggressive. Sometimes, his bloodlust is up to the point where he loses control of himself and is even unable to recall what he had done.

However, Kirito is generally a kind person who is simply misunderstood. Despite the general population opinion towards Beta Testers in SAO, he refused to abandon another player in trouble. This characteristic was only strengthened after the Moonlit Black Cats incident, during which Kirito was responsible for the death of every member within the guild. He also comforts others who are scared or down as a sign of regret and atonement for his past sins. Unlike usual male heroes, is not very dense as is able to tell what the women around him think of him.

Being a very emotional person, Kirito lets his emotions control him from time to time. The deaths of Sachi and Moonlit Black Cats had haunted him up until he married Asuna and found peace in her company. But after he escaped from SAO Kirito almost let the guilt he felt ruin his life. For having temporarily lost his will to live when Asuna's character was killed by off by Heathcliff, the creator of SAO. But by harnessing the resolve that had let him survive the virtual Death Dame thus far, Kirito struck down Heathcliff and put an end to SAO, liberating all players from their virtual prisons and allowing them to return to the real world. Though, he did so at the cost of his own life.

Having woken up outside the Wayne Mansion in his player avatar, Kirito believed he had been played a for a fool and cast into another Virtual prison after having two years freeing himself from his previous one. For having seen Asuna die right before his eyes, he is convinced that his wife is dead and that nothing he can do will bring her back. This mindset filled the Black Swordsman with such profound despair that he attempted suicide by challenging and fighting the strongest monsters he could find in Ihnna Woods and challenged it in the hopes it would kill him. But instead, he found himself rescued by a resident of the Manor. Afterwards, Kirito let himself sink down into the debts of alcoholism in the hopes of drinking himself to death.

But as he hoped to die alone in misery, Kirito instead found the residents of the Mansion rise up and encourage him to live on. With characters like Jenny and Edward Elric helping find a meaning to his life in this new world and live on despite the fact that he had lost everything he had ever cherished in his past life. Now, Kirito works as a Bounty Hunter helping Natsu Dragneel complete dangerous monster hunts in exchange for ridiculous amounts of money.